1. Field of the Invention
The present invention relates to a temperature detecting circuit, a temperature detecting method and a photo-electric conversion apparatus which are constituted, in particular, on a semiconductive substrate.
2. Brief Description of the Related Art
FIG. 7 (PRIOR ART) is a circuit diagram illustrating a conventional constitution of a temperature detection circuit for taking a temperature of a semiconductor substrate. This circuit is constituted of a bipolar transistor Q11 embedded in the semiconductor substrate and a constant current source 11 for flowing a constant current I11 which is connected between a collector electrode of the transistor Q11 and a direct current (referred to as "DC" hereinafter) voltage source Vcc.
In the circuit constituted as mentioned above, the constant current source 11 feeds the constant current I11 to a diode which constitutes the transistor Q11, thereby to generate a forward bias voltage Vf. This forward bias voltage Vf has a temperature characteristics corresponding to the temperature of the semiconductor substrate. Accordingly, one can detect the temperature of the semiconductor substrate from this temperature characteristics.
However, in the conventional example as mentioned above, there exist various problems such as a variance in absolute value of the forward bias voltage Vf of the transistor Q11 which is induced by dispersion in device manufacturing parameters, another variance in the forward bias voltage Vf which is invited by a variation in constant current I11 which is inherent to a performance in constant current characteristics of the constant current circuit 11 and still another variance in temperature characteristics of the transistor Q11 which is introduced by a temperature-dependent variation of the constant current source 11.
Consequently, it is intended to supply the constant current from an external source to eliminate the variances in the constant current I11. However, this intention increases a terminal number and, further, a number of external components, which encounters another problem of an excessive manufacturing cost.
Furthermore, in a case when the circuit is fabricated by using a Complementary Metal Oxide Semiconductor (referred to as "CMOS") device manufacturing process, one of electrodes of the diode is fixed either to a supply voltage or to a grounding potential because of the manufacturing process steps, which results in still another problem that a restriction in output voltage takes place.
On the other hand, in another case when a photo-electric conversion device (referred to as "photosensor" hereinafter) is fabricated on the semiconductor substrate, dark current characteristics which is inherent to the photosensor cannot be neglected and appears as a fixed pattern noise. As a correction measures of the fixed pattern noise, it is proposed to fabricate above-mentioned temperature detection circuit on the same substrate as that the photosensor is formed in, thereby to compensate the pattern noise by using the temperature. However, the correction or the compensation itself not only is unexpectable in precision as well as by cost due to the previously cited problems but also brings about further still another problem that it imposes excessively a restriction on species of employable devices because the device manufacturing processes are limited to that of the photosensor device.